The Electrical Distribution Architecture – Part Ten


In the previous Topic “  The Electrical Distribution Architecture – Part One “, I listed the Tasks required for application of Electrical Distribution architecture design process, they were: 

  • Assigning of electrical installation characteristics, 
  • Assigning of Technological characteristics, 
  • Using Architecture assessment criteria, 
  • Step (1): Choice of distribution architecture fundamentals, 
  • Step (2): choice of architecture details, 
  • Step (3): choice of equipment, 
  • Recommendations for architecture optimization. 

And I explained the first five tasks in the following previous topics: 



Today, I will explain the last two tasks; Step (3): choice of equipment and Recommendations for architecture optimization as follows.



Sixth: Step (3): choice of equipment

The choice of equipment is step (3) in the design of an electrical installation. The aim of this step is to select equipment from the manufacturers’ catalogues.


Note:
  • The choice of technological solutions results from the choice of architecture, the opposite lead to wrong design. 

List of equipment to consider:


  • MV/LV substation, 
  • MV switchboards, 
  • Transformers, 
  • LV switchboards, 
  • Busbar trunking, 
  • UPS units, 
  • Power factor correction and filtering equipment. 

Criteria to consider in equipment choosing:


  • Offer availability per country i.e. the availability of certain ranges of equipment or local technical support, 
  • Previous architecture choices from similar designs of similar projects. 

Note: 
  • The optimal installation will not be the sum of the optimal equipment taken separately, but the result of an optimization of the overall installation. 
  • The detailed selection of equipment is out of the scope of this course but it is include in special courses for equipments like our course “ “ and additional courses for other equipments will be posted shortly. 



Seventh: Recommendations for architecture optimization

These recommendations are intended to guide the designer towards electrical distribution architecture upgrades which allow him to improve assessment criteria. These recommendations include:
  1. On-site work,
  2. Environmental impact,
  3. Preventive maintenance volume,
  4. Electrical power availability.

1- On-site work


To be compatible with the “special” or “critical” work-site time (Review the previous topic 
The Electrical Distribution Architecture – Part Seven ) , it is recommended to limit uncertainties by applying the following recommendations:

  • Use of proven solutions and equipment that has been validated and tested by manufacturers (“functional” switchboard or “manufacturer” switchboard according to the application criticality), 
  • Prefer the implementation of equipment for which there is a reliable distribution network and for which it is possible to have local support (supplier well established), 
  • Prefer the use of factory-built equipment (MV/LV substation, busbar trunking), allowing the volume of operations on site to be limited, 
  • Limit the variety of equipment implemented (e.g. the power of transformers), 
  • Avoid mixing equipment from different manufacturers. 



2- Environmental impact

Review the previous topic" 
The Electrical Distribution Architecture – Part Seven "
The optimization of the environmental assessment of an installation will involve reducing: 

  • Power losses at full load and no load during installation operation, 
  • Overall, the mass of materials used to produce the installation. 

Taken separately and when looking at only one piece of equipment, these 2 objectives may seem contradictory. However, when applied to whole installation, it is possible to design the architecture to contribute to both objectives. The optimal installation will therefore not be the sum of the optimal equipment taken separately, but the result of an optimization of the overall installation.



Example:
Fig (1) gives an example of the contribution per equipment category to the weight and energy dissipation for a 3500 kVA installation spread over 10000m². 


Fig (1)
and the installation has the following conditions:

  • Installation is operating at 50% load on average, with 0,8 power factor. 
  • Site is operating 6500 hours per years : 3 shifts + weekends with reduced activity at night and weekends and full stop 1 month per year for site maintenance and employees holidays. 
  • Power consumption is 9,1 GWh.
  • Reactive power is 6,8 GVARh. This reactive power will be invoiced in addition to power consumption according to local energy contract. 

These data helps to understand and prioritize energy consumption and costs factors as follows:

  • First factor of power consumption is energy usage. This can be optimized with appropriate metering and analysis of loads actual consumption. 
  • Second is reactive energy. This lead to additional load on electrical network. And additional energy invoicing. This can be optimized with power factor correction solutions. 
  • Third is cables. Cable losses can be reduced by appropriate organisation and design of site and use of busbar truncking instead of cables wherever accurate. 
  • MV to LV transformers are fourth with approx. 1% of losses. 
  • MV and LV switchboards come last with approximately 0,25% of losses. 

Generally speaking, LV cables and trunking as well as the MV/LV transformers are the main contributors to operating losses and the weight of equipment used. 



So, Environmental optimization of the installation by the architecture will therefore involve:
  • Reducing the length of LV circuits in the installation, 
  • Clustering LV circuits wherever possible to take advantage of the factor of simultaneity ks (factor Ks will be explained later)
The following table provides the objectives and resources for Environmental optimization of the installation:

Objectives
Resources
Reducing the length
 of LV circuits
Placing MV/LV substations as close as possible to the barycenter of all of the LV loads to be supplied
Clustering LV circuits
When the simultaneity factor of a group of loads to be supplied is less than 0.7, the clustering of circuits allows us to limit the volume of conductors supplying power to these loads.

In real terms this involves:
  • setting up sub-distribution switchboards as close as possible to the barycenter of the groups of loads if they are localized,
  • setting up busbar trunking systems as close as possible to the barycenter of the groups of loads if they are distributed.


The search for an optimal solution may lead to consider several clustering scenarios.

In all cases, reducing the distance between the barycenter of a group of loads and the equipment that supplies them power allows to reduce environmental impact.


As an example fig (2) shows the impact of clustering circuits on reducing the distance between the barycenter of the loads of an installation and that of the sources considered (MLVS whose position is imposed). This example concerns a mineral water bottling plant for which: 

  • The position of electrical equipment (MLVS) is imposed in the premises outside of the process area for reasons of accessibility and atmosphere constraints, 
  • The installed power is around 4 MVA. 


Fig (2)

two solutions can be found :

  • In solution No.1, the circuits are distributed for each workshop. 
  • In solution No. 2, the circuits are distributed by process functions (production lines). 


Without changing the layout of electrical equipment, the second solution allows us to achieve gains of around 15% on the weight of LV cables to be installed (gain on lengths) and a better uniformity of transformer power.

To supplement the optimizations carried out in terms of architecture, the following points also contribute to the optimization:

  • The setting up of LV power factor correction to limit losses in the transformers and LV circuits if this compensation is distributed, 
  • The use of low loss transformers, 
  • The use of aluminum LV busbar trunking when possible, since natural resources of this metal are greater. 



3- Preventive maintenance volume

Recommendations for reducing the volume of preventive maintenance (Review the previous topic The Electrical Distribution Architecture – Part Seven) are as follows: 

  • Use the same recommendations as for reducing the work site time, 
  • Focus maintenance work on critical circuits, 
  • Standardize the choice of equipment, 
  • Use equipment designed for severe atmospheres (requires less maintenance). 



4- Electrical power availability


Recommendations for improving the electrical power availability (Review the previous topic The Electrical Distribution Architecture – Part Seven) are as follows: 



Recommendations to increase the level of availability:
  • Change from a radial single feeder configuration to a two-pole configuration, 
  • Change from a two-pole configuration to a double-ended configuration, 
  • Change from a double-ended configuration to a uninterruptible configuration with a UPS unit and a Static Transfer Switch,
  • Increase the level of maintenance (reducing the MTTR, increasing the MTBF) 



In the next topic, I will introduce Complete Checklist for Designing the Electrical Distribution architecture for any project, in addition to a solved example. So, please keep following.




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